What Happens in Vegas is one of those movies that has no appeal to anyone who is emotionally or chronologically over the age of 16. (And even 16-year-olds may be too mature for it.) For starters, the wannabe-Apatow flick is set in Las Vegas, that overused land of glitz that holds a mystery of sin and drunken fun for frat boys. Plus, particle-board actor Ashton Kutcher and guffawing goof Cameron Diaz are not exactly two stars who send us running to the multiplex. Then there's the plot: Jack (Kutcher), a Brooklyn slacker and Joy (Diaz), a shrewy Wall Street something-or-other, meet in Vegas and get hitched during a drunken blitz. They are ordered to remain married for 6 months by a judge and battle-of-the-sexes comedy hijinks ensue. It might not be a total disaster (it's probably no worse than Made of Honor), but why do they have to drag Rob Corrdery into it? He deserves better! The unanimously bad reviews after the jump.

And thus a by-the-numbers rom-com is born. Alas, What Happens in Vegas ... limps through its first hour or so — where all the "com" is supposed to be — in a knockabout-slapstick mode for which director Tom Vaughan demonstrates no flair whatever. Still, casting will out, and the stars are appealing enough to make the making-up homestretch kinda sweet. No chemistry, mind, and precious few chuckles, but with the only romantic-comedy alternative at the moment being Made of Honor, things could definitely be worse.

As premises go, it makes the heart not so much sink as shrivel. And yet, though it may indeed be synthetic pap with cynical mercenary undercurrents, I'll say this for the movie: we've seen much worse. Neither of the leads, Ashton Kutcher and Cameron Diaz, is a stranger to the slick business of lucrative high-concept comedies - if you catch them looking ecstatic at any point, you wonder if it's just at the box-office prospects.

While Kutcher is reliably believable as a rumpled yet fun-loving slacker, Diaz is considerably less convincing as a steely, MBA-enhanced powerhouse. She may have the jittery energy of a woman who's a stranger to sleep, but with her giggly hair flips, smeary lip gloss and neon-bright micro skirts, she looks more like a party girl staggering home at dawn than a would-be titan of the stock market.

Hokey and forced as it is, What Happens in Vegas eventually settles into a rhythm, maybe because Diaz and Kutcher actually look like they have fun together. Which, unfortunately, is saying a lot. Most of the humor is derived from the same moldy men are from Slobland, women are from Planet Clean clichés, but the movie is just weird and disjointed enough to keep from feeling like an utterly soulless Hollywood product.

Apparently what passes for comedy today is a new form of toilet humor involving the creative use of sinks... What Happens in Vegas has a variation of a joke featured in Baby Mama, as well as a slew of stale riffs on gags and scenarios from a number of comedies, mostly of the romantic variety. It's a story that feels familiar at best, hackneyed at worst, which is surprising and disappointing, as director Tom Vaughan also made last year's Starter for 10, a charming British coming-of-age comedy.

Ashton Kutcher and Cameron Diaz hate on each other with dynamite verve in What Happens in Vegas. The Punch and Judy fireworks get off to an early start, when the two wake up in Las Vegas only to learn that they got hitched during what should have been a sloshed one-night stand. To lay claim to a $3 million slot-machine payoff (one pulled the lever, the other provided the quarter), the two are forced to live together for six months as husband and wife, and I would say that the romantic hilarity just ensues from there, except that Kutcher and Diaz diss each other with such eye-rolling, fang-baring, sexually sarcastic conviction that you may think you've wandered into a dinner-theater revival of Who's Afraid of Virginia Woolf? starring (and rewritten by) Jimmy Kimmel and Sarah Silverman.

The best thing about the fight is how unfairly each wages it, and how the campaigns are based on the classical fault lines of boy-girl cohabitation. That one about the toilet seat (it always has to be down?): The movie addresses it in a clever scene in which Diaz's Joy McNally tries to explain the fundamental difference between the deep concepts of "up" and "down," as if she's explaining quantum theory to a chimp, which she basically is. It's a terrific little set piece, particularly for the expression on her face, which is an odd blend of pity, contempt, boredom, irritation and loathing, all without destroying the fact that she's staggeringly beautiful.

This digression may seem off the point of What Happens in Vegas, but because its director, Tom Vaughan, brings nothing of interest to the movie, including filmmaking, there isn't anything to say other than to note its insulting ugliness and ineptitude. The badly matched Cameron Diaz and Ashton Kutcher mug wildly, waving their limbs like upturned beetles. Ms. Diaz is particularly ill served by the material and the production; she's harshly, at times brutally, lighted and often unflatteringly costumed. It's disheartening that Ms. Diaz doesn't seem to realize that there's no upside to a role that strips away her dignity even as it peels off her clothes, especially when she's playing the shrew. It's no wonder Mr. Kutcher looks so relaxed.